During borehole forming and borehole repair operations, where substantial bottomhole pressures are encountered, and sometimes in various operations associated with the completion of hydrocarbon producing wells, it is necessary to rotate the tool string, tubing string, or drill pipe string while the string is being lowered into or withdrawn from the well bore. This expedient is attained by the provision of a rotating seal member, referred to herein and in the prior art as a stripper rubber, with the stripper being rotatably positioned near the well head in sealed relationship respective of the drill string going into or out of the borehole.
In order to prevent excessive wear of the stripper, it is necessary that the stripper rotate with the piping so that the only significant wear encountered is in the longitudinal movement of the piping relative to the stripper.
In my prior U.S. Pat. No. 3,724,862 to which reference is made for further background of the present invention as well as many additional details of its operation, there is disclosed a blow-out preventer of the rotating type, hereinafter throughout this disclosure referred to as a "BOP of the rotating type", or in some instances, merely a RBOP (rotating blow-out preventer).
Throughout this disclosure, the term tubing string or piping refers to a drill string, including the various tools attached thereto, such as a stabilizer, a drill collar, as well as the kelly, and further includes other tubular goods such as production tubing, instrument packages, jars, fishing tools, and the like. The drill or tool string is generally circular or round in configuration, except for the kelly which usually is noncircular in configuration. Hence, the stripper rubber must deform sufficiently to sealingly engage of outer peripheral surface of each of these recited members.
In the various prior art rotary drilling head assemblies, or RBOP, the stripper is usually affixed to a lower marginal portion of the rotating sleeve, thereby rendering replacement or repair extremely difficult when the head is operatively affixed to the upper terminal end of the well bore.
In my previously referred to issued patent, the rotating stripper is affixed to the upper terminal end of the rotating sleeve by means of the mounting plate bolted onto structure associated with the sleeve. Substitution of one stripper for another must sometimes be carried out several times each trip the tool string makes into the borehole, and accordingly, it is desirable to be able to rapidly renew the stripper, or to substitute one size stripper for another. Moreover, it is desirable to provide a reliable seal means at the interface formed between the fixed and rotating sleeves and to protect the bearing surfaces which rotatably secure the rotating sleeve from up or downhole thrust by the provision of improvements in the seal and lubrication system therefor. It is also desirable to have provisions by which two divergent sizes of tubing string can be sealingly run uphole and downhole through the RBOP without resorting to other means of sealing the upper annulus between the tool string and the wall of the well bore.